command: Enable reading remote-enabled state

command/meta.go

@@ -42,6 +42,8 @@ type Meta struct {
 	oldUi cli.Ui
 
 	// useRemoteState is enabled if we are using remote state storage
+	// This is set when the context is loaded if we read from a remote
+	// enabled state file.
 	useRemoteState bool
 
 	// statePath is the path to the state file. If this is empty, then
@@ -106,25 +108,16 @@ func (m *Meta) Context(copts contextOpts) (*terraform.Context, bool, error) {
 		}
 	}
 
-	// Load up the state
-	var state *terraform.State
+	// Load the statePath if not given
 	if copts.StatePath != "" {
-		f, err := os.Open(copts.StatePath)
-		if err != nil && os.IsNotExist(err) {
-			// If the state file doesn't exist, it is okay, since it
-			// is probably a new infrastructure.
-			err = nil
-		} else if err == nil {
-			state, err = terraform.ReadState(f)
-			f.Close()
-		}
-
-		if err != nil {
-			return nil, false, fmt.Errorf("Error loading state: %s", err)
-		}
+		m.statePath = copts.StatePath
 	}
 
 	// Store the loaded state
+	state, err := m.loadState()
+	if err != nil {
+		return nil, false, err
+	}
 	m.state = state
 
 	// Load the root module
@@ -171,6 +164,43 @@ func (m *Meta) UIInput() terraform.UIInput {
 	}
 }
 
+// laodState is used to load the Terraform state. We give precedence
+// to a remote state if enabled, and then check the normal state path.
+func (m *Meta) loadState() (*terraform.State, error) {
+	// Check if we remote state is enabled
+	localCache, _, err := remote.ReadLocalState()
+	if err != nil {
+		return nil, fmt.Errorf("Error loading state: %s", err)
+	}
+
+	// Set the state if enabled
+	var state *terraform.State
+	if localCache != nil {
+		state = localCache
+		m.useRemoteState = true
+	}
+
+	// Load up the state
+	if m.statePath != "" {
+		f, err := os.Open(m.statePath)
+		if err != nil && os.IsNotExist(err) {
+			// If the state file doesn't exist, it is okay, since it
+			// is probably a new infrastructure.
+			err = nil
+		} else if m.useRemoteState && err == nil {
+			err = fmt.Errorf("Remote state enabled, but state file '%s' also present.", m.statePath)
+			f.Close()
+		} else if err == nil {
+			state, err = terraform.ReadState(f)
+			f.Close()
+		}
+		if err != nil {
+			return nil, fmt.Errorf("Error loading state: %s", err)
+		}
+	}
+	return state, nil
+}
+
 // PersistState is used to write out the state, handling backup of
 // the existing state file and respecting path configurations.
 func (m *Meta) PersistState(s *terraform.State) error {

command/meta_test.go

@@ -255,3 +255,78 @@ func TestMeta_persistRemote(t *testing.T) {
 		t.Fatalf("backup should exist")
 	}
 }
+
+func TestMeta_loadState_remote(t *testing.T) {
+	tmp, cwd := testCwd(t)
+	defer testFixCwd(t, tmp, cwd)
+
+	err := remote.EnsureDirectory()
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	s := terraform.NewState()
+	s.Serial = 1000
+	if err := remote.PersistState(s); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	m := new(Meta)
+	s1, err := m.loadState()
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	if s1.Serial < 1000 {
+		t.Fatalf("Bad: %#v", s1)
+	}
+
+	if !m.useRemoteState {
+		t.Fatalf("should enable remote")
+	}
+}
+
+func TestMeta_loadState_statePath(t *testing.T) {
+	tmp, cwd := testCwd(t)
+	defer testFixCwd(t, tmp, cwd)
+
+	m := new(Meta)
+
+	s := terraform.NewState()
+	s.Serial = 1000
+	if err := m.persistLocalState(s); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	s1, err := m.loadState()
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	if s1.Serial < 1000 {
+		t.Fatalf("Bad: %#v", s1)
+	}
+}
+
+func TestMeta_loadState_conflict(t *testing.T) {
+	tmp, cwd := testCwd(t)
+	defer testFixCwd(t, tmp, cwd)
+
+	err := remote.EnsureDirectory()
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	m := new(Meta)
+
+	s := terraform.NewState()
+	if err := remote.PersistState(s); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	if err := m.persistLocalState(s); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	_, err = m.loadState()
+	if err == nil {
+		t.Fatalf("should error with conflict")
+	}
+}